1. Field of the Invention
The present invention relates to a flow measuring device of the type making use of Karman's vortices. More particularly, this invention relates to a vortex-shedding flow-measuring device wherein the frequency of vortex shedding is sensed by a capacitance detector.
2. Description of the Prior Art
There are many prior art disclosures showing various kinds of vortex-shedding devices for measuring fluid flow rate. In such devices, a bar or other obstacle in the fluid flow path sheds vortices alternately from opposite sides thereof. Such vortex shedding sets up vibrations or oscillations in the vortex generating body, and it is known that the frequency of those vibrations can be measured to provide an indication of the velocity of fluid flow. Devices of the general type are shown in U.S. Pat. No. 3,972,232, where a piezoelectric pickup is used for determining the frequency of vortex shedding. Devices for detecting the vibrations of the obstacle by means of capacitance sensors is disclosed in U.S. Pat. No. 3,927,566, particularly at FIGS. 2 and 3. Still another device is shown, for example, at FIGS. 6 thru 8 of U.S. Pat. No. 4,186,599.
In these known devices, the measurement is made at a high sensitivity because it relies upon the detection of vibration of the body or obstacle. However, in these known devices the measurement can be adversely affected by mechanical vibrations which are transmitted through the pipe.